In recent years, it has become possible to diagnose many diseases from body fluid such as blood or urine. However, there is a limit on the amount of body fluid that can be used for diagnosis (hereinafter, referred to as a sample). Therefore, it has become important to develop a device that makes it possible to obtain as much information as possible (e.g., the degree of progression of disease or the early detection of disease) from a small amount of sample.
A device has been proposed which uses a micro-fluid chip including a resin substrate and two or more microchannels formed on the resin substrate. At the tip end of each of the microchannels provided on the substrate of the device, a detection section is provided which includes an antibody or the like that reacts with an antigen that causes each disease. Therefore, the use of such a device makes it possible to diagnose two or more diseases by a single analysis. However, such a device requires a driving means such as a pump to send a sample into the channels, which causes a problem that the device requires a certain amount of sample and increases in size.
In recent years, a micro-fluid chip that requires no pump has been proposed. A typical example of such a micro-fluid chip is a paper-made micro-fluid chip whose microchannels are made of paper. Such a paper-made micro-fluid chip is based on a technique using the water absorbability of paper, that is, capillarity. More specifically, when a liquid sample is supplied to the base ends of the channels of the paper-made micro-fluid chip, the sample automatically moves from the base ends of the channels to detection sections provided at the tip ends of the channels. Therefore, two or more diseases can be diagnosed by a single analysis without using a pump for sending a sample. In addition, there is an advantage that disease diagnosis can be performed only by the paper-made micro-fluid chip.
As a method for forming such paper-made microchannels as described above, a method using wax printing or a method using photolithography has been proposed.
In the case of wax printing, a sheet of paper is impregnated with a hydrophobic wax along the side edges of channels on the sheet of paper. As a result, as shown in FIG. 6(A) and FIG. 6(B), paper-made microchannels are formed by forming channel walls made of the hydrophobic wax.
In the case of photolithography, paper is immersed in a photoresist (photosensitive resin), and is then masked so that a desired channel pattern can be formed, and is then exposed to UV or the like. Then, the unexposed photoresist is removed. As a result, as shown in FIG. 6(C) and FIG. 6(D), paper-made microchannels are formed by forming channel walls made of the cured resin (cured part).
However, in the case of such paper-made microchannels formed by the above method, a sample containing a plurality of components moves through all the channels. Therefore, there is a possibility that the accuracy of measurement of a desired component at each of the detection sections is reduced due to the influence of components other than the desired component contained in the sample.
Meanwhile, a micro-fluid chip has been proposed which has three-dimensional channels formed by photolithography (e.g., Patent Document 1).
As shown in FIG. 7 (A) and FIG. 7 (B), the three-dimensional micro-fluid chip described in Patent Document 1 has a multi-layer structure in which slips of paper processed by photolithography are coupled together as top, middle, and bottom layers. The slip of paper as a middle layer is formed to have holes through which the front and back surfaces thereof communicate with each other so that only a predetermined channel in the upper layer and a predetermined channel in the bottom layer are connected together through the holes. Further, Patent Document 1 describes that a filter is provided in the holes formed in the middle layer.
Therefore, as shown in FIG. 7(C), when two samples are supplied to their respective channels, which three-dimensionally intersect with each other, of the three-dimensional micro-fluid chip described in Patent Document 1, both the samples are allowed to move from the sample supply sections to the tip ends of the channels without being mixed together. Therefore, the use of the three-dimensional micro-fluid chip described in Patent Document 1 makes it possible to analyze more samples and improve the accuracy of a test due to a filtering function as compared to a case where two-dimensional channels are formed in a chip of the same size.